The present invention relates generally to a collision avoidance method and system and more particularly to a method of and system for detecting the presence of an object within a range of a reference point and for determining the distance between the object and the reference point and, if the object is within a predetermined distance from the reference point, activating an alarm.
A typical construction or mining area can include heavy machinery, such as bulldozers, front loaders, cranes, surface and subsurface mining equipment and other construction vehicles, as well as construction workers working in the area on foot. Such an environment, where the equipment, as well as the work being done, is very loud, can be extremely dangerous for those construction workers which are working on foot in close proximity with the construction vehicles. In fact, in 1996, 461 non-occupant fatalities were reportedly caused by heavy and medium sized construction vehicles. In the subsurface mining industry alone, there are an average of five collision deaths a year, and many more injuries due to collisions between construction vehicles and construction pedestrians. This is mainly because of the type of working environment, which can have varying terrain which can hamper a construction vehicle operator""s view of the surrounding area, and the design of the construction vehicles, which is not necessarily geared toward providing the operator with an optimal view of his or her surroundings.
Prior art attempts at preventing construction site collisions include equipping construction vehicles with beepers which are activated when the vehicle is shifted into reverse to warn pedestrians of the vehicle""s movement. While this type of warning system can be helpful, it does not alarm the driver of the vehicle of the presence of pedestrians and, in a construction environment where very loud vehicles are being operated and loud work such as blasting, digging, etc. is being performed, it is possible that a pedestrian in potential danger may not hear the beeper.
Other attempts at providing safety for construction pedestrians include electromagnetic signal-based systems (i.e. RF, infrared, optical) in which an alarm is placed proximate the operator of the vehicle and a detection device is mounted external to the vehicle, typically at the rear of the vehicle. In one type of system, the pedestrian wears a passive receiver device for receiving an interrogation signal output by the detection device and which transmits a response signal to the detection device upon receiving the interrogation signal. While such systems may be more effective than the beeper-type systems, passive RF receivers require large electric field strengths to be output by the detection device. This type of system can be very dangerous if used in the presence of explosives. Infrared systems are hampered by high levels of background noise (heat sources) which makes them unsuitable for many applications in the construction and mining trades as well as in fire and rescue situations. Optical systems are limited strictly to line-of-sight detection, which limits their use in a similar fashion. Furthermore, none of these systems are easily made to determine range at reasonably close distances due to the extremely short time of flight of the signals.
Alternatively, the device worn by the pedestrian may be an active transmitter device which periodically transmits a signal to a receiver mounted on the vehicle. Upon receiving the signal from the pedestrian, the receiver may sound an alarm to notify the operator of the presence of the pedestrian. While RF versions of this type of system do not require the large electric field strengths required by the passive system, in general these systems suffer from the same problems as the passive tag types, are not able to determine the distance of the pedestrian from the receiver, and are thus more likely to cause false alarms. Typically, they infer proximity between the receiver and transmitting device through measurement and/or signal processing of the received signal intensity, which does not allow distance measurement to a level of accuracy sufficient to insure safety.
The present invention is directed to a collision avoidance system including a reader device attached to a moving vehicle such as a construction vehicle and a tag device, which is worn on the body of a construction pedestrian. The reader device periodically transmits an ultrasonic pulse which, if the pedestrian is within a predetermined range, is received by the tag device. The tag device, in response to the reception of the ultrasonic pulse from the reader device, transmits an RF response pulse to the reader device. The reader device determines the distance of the pedestrian from the reader device based on the elapsed time between the transmission of the ultrasonic pulse and the reception of the RF pulse. Varying modes of alarm may be activated, based on the distance of the pedestrian from the reader device. A visual and/or audible alarm device is located proximate the operator of the vehicle. It should be noted that for the purposes of this writing, it is assumed that the tag device is worn by a pedestrian and the reader device is mounted on a moving vehicle. However, a tag and reader pair may be installed on any number of objects, of any type, which one wishes to protect from collisions. Furthermore, any number of tags may be installed on multiple objects within the fields of any number of readers, to support collision avoidance between those objects with readers and those objects with tags. It is further noted that the present invention describes ultrasonic transmissions in air, as it is expected this will be appropriate for the largest number of applications. However, operation of the system in other transmission media, such as through smoke, debris, or underground, is possible with straightforward changes to account for ultrasonic transducer interfacing to the medium and to account for the speed of sound in the medium.
According to one embodiment of the invention, a presence detection system is disclosed, including a reader device attached to a first body, and a tag device attached to a second body. The reader device has an ultrasonic transducer for generating and transmitting ultrasonic pulses at a first rate of occurrence; an RF receiver for receiving an RF signal; and a microcontroller coupled to the ultrasonic transducer and the RF receiver for receiving signals from the RF receiver and for controlling the operation of the ultrasonic transducer and the RF receiver. The tag device has an ultrasonic receiver for receiving ultrasonic pulses from the ultrasonic transducer of the reader device; and an RF pulse generator for generating and transmitting an RF pulse. The microcontroller in the reader device instructs the ultrasonic transducer to generate and transmit the ultrasonic pulses; the ultrasonic receiver of the tag device receives at least one of the ultrasonic pulses; the ultrasonic receiver in the tag device triggers the RF signal generator to transmit an RF pulse; the RF receiver of the reader device receives the RF signal; and the microcontroller detects the presence of the tag device based on the reception of the RF pulse.
The tag device may further include a timing circuit, which may be a second microcontroller, which operates to trigger the RF pulse generator of the tag device to transmit an RF pulse at a second rate of occurrence, the second rate of occurrence being different from the first rate of occurrence. One of the ultrasonic pulses transmitted by the ultrasonic transducer may be transmitted at a time xcfx841, and the RF pulse resulting from the reception of the ultrasonic pulse by the ultrasonic receiver in the tag device may be received by the RF receiver of the reader device at a time xcfx842; wherein the microcontroller determines a distance D between the reader device and the tag device according to the equation:
D=VS (xcfx842xe2x88x92xcfx841); 
where VS is the velocity of sound in air. The timing circuit, or second microcontroller, may generate a timing pulse to trigger the RF transmitter to transmit an RF pulse at the second rate of occurrence when the ultrasonic receiver does not receive an ultrasonic pulse from the ultrasonic transducer within a predetermined period of time from the reception of a previous ultrasonic pulse. As an example, the first rate of occurrence may be three pulses per second and the second rate of occurrence may be one pulse per second. The first body may be a movable vehicle having the reader device attached thereto and the second body may be a person having the tag device attached thereto. The system may further include an alarm device coupled to the first microcontroller, wherein the first microcontroller activates the alarm device upon detecting the presence of the tag device, or when the tag device is determined to be within a predetermined range. The alarms may vary in type depending on the how range, rate of range closure, or simple presence detection are prioritized for a given application. The visual indicator may include a plurality of LEDs in which the number of LEDs that are triggered increases as the distance between the reader device and the tag device decreases. The audible indicator may include a beeper in which the frequency of beeps output by the beeper increases as the distance between the reader device and the tag device decreases. The timing circuit may include a microcontroller which is programmed trigger the RF pulse generator at predetermined intervals and when the ultrasonic pulse is received by the ultrasonic receiver.
According to another embodiment of the invention, a system for determining the distance between a first object and a second object is disclosed including:
a reader device mounted on the first body, the reader device including an ultrasonic transducer, a microcontroller and an RF receiver; and
a tag device mounted on the second object, the tag device including an ultrasonic receiver and an RF pulse transmitter;
wherein, in response to receiving an ultrasonic pulse transmitted by the reader device at a time TA, the tag device transmits an RF pulse, which is received by the reader device at a time TB, and the microcontroller of the reader device determines the distance D between the first and second objects according to the equation:
D=VSxc2x7(TBxe2x88x92TA); 
where VS is the velocity of sound in air.
According to another embodiment of the invention, a method of detecting the presence of an object is disclosed including:
A. transmitting ultrasonic pulses at a first rate of occurrence from a first location;
B. receiving at least one of the ultrasonic pulses at a second location;
C. transmitting an RF pulse in response to the reception of the ultrasonic pulse at the second location;
D. receiving the RF pulse at the first location; and
E. detecting the presence of the object at the second location based on the reception of the RF pulse at the first location.
The method may further include determining a distance of the object from the first location based on an elapsed time between the transmission of the ultrasonic pulse from the first location to the reception of the RF pulse at the first location. The method may further include activating an alarm when the distance between the object and the first location is less than a predetermined range. The activating step may include at least one of illuminating a series of LEDs and activating a beeper.
According to yet another embodiment of the invention, a method for determining a distance between a first object location and a second object location is disclosed, including:
A. transmitting an ultrasonic pulse from the location of the first object at a time TA;
B. receiving the ultrasonic pulse at the location of the second object;
C. transmitting an RF pulse from the second object location in response to the reception of the ultrasonic pulse;
D. receiving the RF pulse at the first object location at a time TB; and
E. determining the distance D between the first object location and the second object location according to the equation:
D=VSxc2x7(TBxe2x88x92TA); 
where VS is the velocity of sound in air.